Cognitive Effects of Taurine and Related Sulphur-Containing Amino Acids: A Systematic Review of Human Trials and Considerations for Plant-Based Dietary Transitions

Background: As diets shift towards more plant-based patterns, nutrients mainly supplied by animal-sourced foods are under increased scrutiny, including sulphur-containing amino acids (SCAAs) such as taurine (TAU), methionine (MET) and cysteine (CYS), which support neuroprotection, antioxidant defences and cellular signalling and may therefore be relevant for cognitive health. Method: This systematic review examined the relationship between SCAA supplementation and cognitive function in randomised controlled trials (RCTs). PubMed, EMBASE and PsycINFO were searched in July–August 2024 and updated in September 2025 (PROSPERO: CRD42024574453) for RCTs assessing SCAA supplementation or depletion and cognitive or psychological outcomes. Data were narratively synthesised with explicit consideration of contextual factors (e.g., co-ingested ingredients, exercise state, testing conditions). Results: Eight RCTs (N = 244) were included; all investigated TAU, with no MET or CYS trials. All used acute single-dose interventions, mostly in crossover designs, assessing core cognitive domains and mood. Across trials, acute TAU doses (typically 1–3 g; up to ~50 mg/kg) produced at best small, isolated cognitive benefits, with most outcomes unchanged. Combinations of TAU with caffeine more consistently improved performance but did not clarify TAU’s independent contribution, and effects on mood and wellbeing were generally small, inconsistent and only apparent under specific conditions (e.g., co-ingestion with caffeine, exercise or sleep loss. No trial characterised habitual diet or baseline SCAA status or recruited participants with low animal-source food intake, so cognitive vulnerability under reduced SCAA intake remains untested. Conclusion: Acute TAU trials provide limited evidence of short-term cognitive or mood benefits and do not clarify whether lower SCAA intake in plant-based diets affects cognition or mood. Longer-term, well-powered studies that characterise habitual diet and SCAA status, include MET and CYS, and assess cognition and mood in populations with lower animal-source food intake are needed to determine whether SCAAs should form part of strategies to support brain health as diets shift towards plant-based eating.